// Copyright (C) 2012-2015 ChaosForge Ltd
// http://chaosforge.org/
//
// This file is part of Nova libraries. 
// For conditions of distribution and use, see copying.txt file in root folder.
//
// TODO: support for write operations, see http://www.mr-edd.co.uk/blog/beginners_guide_streambuf

#include "nv/io/std_stream.hh"
#include "nv/stl/math.hh"
#include "nv/stl/utility.hh"

using namespace nv;

std_streambuf::std_streambuf( stream* source, bool owner /*= false*/, std::size_t bsize /*= 256*/, std::size_t put_back /*= 8 */ )
	: m_stream( source )
	, m_owner( owner )
	, m_buffer( nv::max(bsize, put_back) + put_back )
	, m_put_back( nv::max( put_back, std::size_t( 1 ) ) )
{
	char *end = &m_buffer.front() + m_buffer.size();
	setg( end, end, end );
}

std_streambuf::~std_streambuf()
{
	if ( m_owner )
	{
		delete m_stream;
	}
}

std_streambuf::int_type std_streambuf::underflow()
{
	if (gptr() < egptr())
	{
		// buffer not exhausted
		return traits_type::to_int_type(*gptr());
	}

	char *base = &m_buffer.front();
	char *start = base;

	if (eback() == base) // true when this isn't the first fill
	{
		// Make arrangements for putback characters
		std::copy( egptr() - m_put_back, egptr(), base ); 
		start += m_put_back;
	}

	// start is now the start of the buffer, proper.
	size_t n = m_stream->read( start, 1, m_buffer.size() - static_cast<size_t>(start - base) );
	if (n == 0)
	{
		return traits_type::eof();
	}

	// Set buffer pointers
	setg(base, start, start + n);

	return traits_type::to_int_type(*gptr());
}